Generally, keeping a working stage and the surface of a substrate clean is crucial for fabricating a liquid crystal display (LCD), for any particle existing thereon may degrade the quality and stability of the process, or even result in damages to the working stage and the product.
Especially, during an alignment film coating process of the LCD back-end process, the foreign objects existing on the working stage or on the surface of the substrate will deter the coating process from being smoothly performed, thus effecting the quality of the alignment film and lowering the quality control of the LCD. Further, the foreign particles may cause damages to coating rollers or other equipment, and even break a glass substrate, thus effecting productivity and reducing the operation life of the equipment.
Hence, besides keeping the working stage and the surface of the substrate clean, a foreign objects detecting step is also needed. Generally, before the manufacturing process starts, the foreign objects detecting step is first performed onto the working stage or the substrate surface, wherein if any foreign object is detected, then the manufacturing process is stopped, thus effectively preventing the foreign objects on the working stage or the substrate surface from damaging the products and equipment.
The conventional foreign objects detecting step uses a laser beam or diffusion light to perform detection on the working stage or the substrate surface, wherein the foreign objects are monitored in accordance with the intensity changes of light diffusion, reflection or refraction. However, by using the diffusion light, the object size that can be identifies is rather limited, and the precision of detecting the foreign objects thereby is not sufficient to be suitable us in a display panel or even semiconductor manufacturing process. Therefore, the current foreign objects detecting method mostly adopts the laser source so as to increase the precision of detecting the foreign objects.
However, the current foreign objects detecting methods all place a laser source above a working stage or a substrate, and directly irradiate the surface of the working stage or substrate, and then observe the states of the laser light before and after reflection or diffusion and refraction. The laser light is interfered simultaneously by the working stage, the substrate and the foreign objects, and thus, if the refractive indexes of the foreign objects located on the working stage and the substrate are close to those of the working stage and the substrate, then the foreign objects cannot be detected. For example, the refractive index of the glass scrap is the same as that of the glass substrate. Further more, since the even smaller foreign particles have less apparent degrees of interference against the laser light, and are susceptible to the inference from the working stage and the substrate, they are hardly to be detected. Further, the laser light has to be frequently calibrated effecting accordance with the materials forming the working stage and the substrate, thus resulting in many errors of the actual measurement and limiting the detection precision.